ZHCSMW2B December   2021  – December 2022 LM5123-Q1

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 说明（续）
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Device Enable/Disable (EN, VH Pin)
      2. 8.3.2  High Voltage VCC Regulator (BIAS, VCC Pin)
      3. 8.3.3  Light Load Switching Mode Selection (MODE Pin)
      4. 8.3.4  VOUT Range Selection (RANGE Pin)
      5. 8.3.5  Line Undervoltage Lockout (UVLO Pin)
      6. 8.3.6  Fast Restart using VCC HOLD (VH Pin)
      7. 8.3.7  Adjustable Output Regulation Target (VOUT, TRK, VREF Pin)
      8. 8.3.8  Overvoltage Protection (VOUT Pin)
      9. 8.3.9  Power Good Indicator (PGOOD Pin)
      10. 8.3.10 Dynamically Programmable Switching Frequency (RT)
      11. 8.3.11 External Clock Synchronization (SYNC Pin)
      12. 8.3.12 Programmable Spread Spectrum (DITHER Pin)
      13. 8.3.13 Programmable Soft Start (SS Pin)
      14. 8.3.14 Wide Bandwidth Transconductance Error Amplifier and PWM (TRK, COMP Pin)
      15. 8.3.15 Current Sensing and Slope Compensation (CSP, CSN Pin)
      16. 8.3.16 Constant Peak Current Limit (CSP, CSN Pin)
      17. 8.3.17 Maximum Duty Cycle and Minimum Controllable On-Time Limits
      18. 8.3.18 Deep Sleep Mode and Bypass Operation (HO, CP Pin)
      19. 8.3.19 MOSFET Drivers, Integrated Boot Diode, and Hiccup Mode Fault Protection (LO, HO, HB Pin)
      20. 8.3.20 Thermal Shutdown Protection
    4. 8.4 Device Functional Modes
      1. 8.4.1 Device Status
        1. 8.4.1.1 Shutdown Mode
        2. 8.4.1.2 Configuration Mode
        3. 8.4.1.3 Active Mode
        4. 8.4.1.4 Sleep Mode
        5. 8.4.1.5 Deep Sleep Mode
      2. 8.4.2 Light Load Switching Mode
        1. 8.4.2.1 Forced PWM (FPWM) Mode
        2. 8.4.2.2 Diode Emulation (DE) Mode
        3. 8.4.2.3 Forced Diode Emulation Operation in FPWM Mode
        4. 8.4.2.4 Skip Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Application Ideas
      3. 9.2.3 Application Curves
    3. 9.3 System Example
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 第三方产品免责声明
    2. 12.2 接收文档更新通知
    3. 12.3 支持资源
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 术语表
  13. 13Mechanical, Packaging, and Orderable Information

封装选项

请参考 PDF 数据表获取器件具体的封装图。

机械数据 (封装 | 引脚)
  • RGR|20
散热焊盘机械数据 (封装 | 引脚)
订购信息

8.3.13 Programmable Soft Start (SS Pin)

The soft-start feature helps the converter gradually reach the steady state operating point. To reduce start-up stresses and surges, the device regulates the error amplifier reference to the SS pin voltage or the TRK pin voltage (VTRK), whichever is lower.

The internal 20 μA soft-start (ISS) current turns on 120 μs after the VCC pin crosses VVCC-UVLO. ISS gradually increases the voltage on an external soft-start capacitor (CSS). This results in a gradual rise of the output voltage.

In FPWM mode, the device forces diode emulation while the SS pin voltage is less than 1.5 V. When the SS pin voltage is greater than 1.5 V, the device changes the zero current detection (ZCD) threshold gradually from 4 mV to –145 mV to achieve a smooth transition from diode emulation to FPWM mode.

GUID-20200814-CA0I-Z9M6-Q4C3-6TCQQVDKVRXH-low.gif Figure 8-12 Soft Start and Smooth Transition to FPWM

In boost topology, the soft-start time (tSS) varies with the input supply voltage because the boost output voltage is equal to the boost input voltage at the beginning of the soft-start switching. tSS in boost topology is calculated in Equation 10.

Equation 10. t S S = V T R K × C S S 20 μ A × 1 - V S U P P L Y V L O A D

In general, it is recommended to choose a soft-start time long enough so that the converter can start up without going into an overcurrent state. If the device is used for a pre-boost in automotive application, it is recommended to use 100-pF CSS to reach steady state as soon as possible.

The device also features an internal SS-to-FB clamp (VSS-FB), which clamps SS 55 mV above FB and is activated if 256 consecutive switching cycles occur with current limit. The SS-to-FB clamp is deactivated if 32 consecutive switching cycles occur without exceeding the current limit threshold. This clamp helps to minimize surges after output shorts or over load situations. The device can enter deep sleep mode when SS is greater than 1.5 V. It is not recommended to pulldown SS to stop switching.